This invention is directed to silica nanoparticles agglomerated into a three-dimensional web-like structure. The silica is obtained by laser ablation of a silicon metal target in an oxygen-containing atmosphere. The morphology consists of agglomerated nanoparticles about 10-20 nanometers (nm) in diameter, which are fused together into an open three-dimensional network with high surface area.
The synthesis and characterization of nanoparticles has received attention in recent years for their use as catalysts. Silica nanoparticles are materials with many applications since silica is inherently thermally stable. Furthermore, the morphology of amorphous silica powders and porous gels is of interest for improving mechanical and electrical properties of materials where silica is used.
A range of nanoparticles has been produced by chemical and physical methods. The most common physical methods involve gas condensation techniques where oven sources are used to produce metal vapors. In spite of success with this method, there are still problems and limitations, such as reactions between metal vapors and oven materials, inhomogeneous heating of the source limiting control of particle size and distribution, incomplete vaporization of refractory metals due to low vapor pressure, and range of control of the composition of the mixed metal particles due to the difference in composition between the alloys and the mixed vapors.
The advantages over other heating methods which laser vaporization techniques provide are the production of high density metal vapor within a short time (10.sup.-8 s), the generation of directional high speed metal vapor from a solid target for directional deposition of the particles, and control of evaporation from specific spots on a target as well as simultaneous or sequential evaporation of several different targets. Some of these advantages have been demonstrated in the synthesis of ultrafine metal particles, but control of the nucleation process which strongly affects particle size, composition, and morphology of the deposited material, has not yet been achieved.
According to the present invention, we have discovered a new form of silica in which nanoparticles aggregate into a unique web-like microstructure. This web-like nanoparticle silica exhibits blue photoluminescence upon irradiation with ultraviolet light. The web-like nanoparticle silica with controlled size and composition is synthesized with a technique that combines the advantages of pulsed laser vaporization with controlled condensation in a diffusion cloud chamber under well defined conditions of temperature and pressure. The various forms of nanoparticle silica according to the invention are suitable for use in building non-linear optical devices employed in the communications industry, and for building flat-panel displays.